This invention relates to hydroprocessing catalysts and methods of making them.
As petroleum reserves dwindle, refiners must process the heavier feedstocks, high in alphaltenes, metals and sulfur, that remain. These feedstocks are notable because they contain high levels of impurities and low hydrogen to carbon ratios. Most methods of treating these feedstocks involve treating them with molecular hydrogen in the presence of a hydroprocessing catalyst. The typical hydroprocessing catalyst is a Group VIII metal and a Group VIB metal (Handbook of Chemistry and Physics, 51st Ed., Chemical Rubber Co., Cleveland, Ohio, 1970) supported on a refractory inorganic oxide. It is known that pore sizes, catalyst surface area and amounts of metals all contribute to the catalyst's activity and that a catalyst which is very active for one feedstock may be inactive or very rapidly fouled by another feedstock. Therefore, it has been suggested that poor quality feedstocks be passed over beds of several different catalysts, thereby most advantageously utilizing each particular catalyst and removing the impurities in the feedstock that might deactivate the next catalyst in the sequence. Typically, the first catalyst in such a sequence has a large average pore diameter and a significant fraction of the pore volume as macropores, with a relatively low catalytic metals loading. As used herein, "macropore" refers to pores having diameters larger than 1000 .ANG.. Such a catalyst is suitable for removing some contaminant metals, asphaltenes, and sulfur from the feedstock. The feedstock so processed is then contacted with a second catalyst having a smaller average pore diameter and a small macropore volume fraction, with a higher catalytic metals loading. Such a catalyst is more active for removing sulfur. Other smaller pored and even more active catalysts may be added in turn, removing yet more sulfur and thereby providing a relatively high-quality, low-impurity product, suitable for hydrocracking or distillation into products.
This invention provides catalyst particles that are individually layered thereby providing the effect of several beds of different catalyst in one bed of catalyst.